Vector Spaces & Bases · Hard problem

Let $B = \{(1,1,1),\ (1,-1,0),\ (0,1,-1)\}$ and $C = \{(1,0,0),\ (1,1,0),\ (1,1,1)\}$, both bases of $\mathbb{R}^3$. A vector $\mathbf v$ has $B$-coordinates $(2,-1,1)$. Find the first (leading) $C$-coordinate of $\mathbf v$.